652 HERBIVOROUS MARSUPIALS 



Our knowledge is at present confined to two specimens of lower 

 jaws,* evidently referable to two distinct species, extremely unequal 

 in size, and otherwise distinguishable. The largest, P. Becklesii (fig. 1), 

 was about as big as the English squirrel or the flying phalanger of 

 Australia (Petaurus Australis, Waterhouse). The skeleton of this 

 phalanger (named P. macrurus, No. 1849, Museum of College of Sur- 

 geons) measures 15 inches in length, exclusive of the tail, which is more 

 than 11 inches long. The smaller fossil (P. minor, fig. 2), having 

 only half the linear dimensions of the other, was probably only 1-1 2th 

 of its bulk. To the geologist, however, it is perhaps the more interest- 

 ing of the two, as Dr. Falconer has recog- 

 Fi s- 8 - nized in its two back molars (c, d, fig. 2) an 



unmistakable resemblance to those of the 

 Triassic Microlestes (5, c, fig. 3). 



Of this most ancient of known fossil mam- 

 malia an account is given in the text at p. 

 Teeth of Mcroiestes antiquw, 341 vvitla. illustrations, anions which, how- 



Plteninger, from the Upper ' 1 



Trias of" Wirtemburc. ever, there was no figure of the crown of 



0. Crown of the smaller molar (&, . . . , . , . . , , .., 



fig. 441, p. 841, of the text) the larger molar, which is now added, with 

 c Crown oAarger tooth (fig. 442 a new illustration of the crown of the smaller 



ffiI^o 1 S£S.iLd! ecrow,, t00th - No naturalist on the Continent to 

 whom I had previously shown casts and 

 drawings of these teeth, had been able to give any feasible conjecture 

 as to its affinities. Plieninger considered it to be predaceous, whence 

 the name ; others fancied they saw some likeness in the form of its 

 grinders to those of an omnivorous pachyderm, as well as of an Insec- 

 tivore ; while Professor Owen, at once recognizing the mammalian char- 

 acter of the' double-fanged teeth, said they were distinct from any type 

 known to him. When these grinders of Microlestes (fig. 3) are com- 

 pared to those of Plagiaulax minor (d, c, fig. 2), the reader will agree 

 with Dr. Falconer, that "had they all been found detached in the 

 same slab they might have been taken for back and front, or for upper 

 and lower teeth of the same or some cognate species, the essential 

 characters of the crown being identical ;f whereas, had the last molax 

 and last pre-molar of Plagiaulax been found fossil under similar cir- 

 cumstances, they would in all probability have been taken for teeth not 

 merely of different genera, but even of different orders of mammalia." 



Two principal questions, observes Dr. Falconer, deserve our con- 

 sideration with reference to. Plagiaulax; namely, first, Was it mar- 



* Three additional specimens of P. Becklesii have since arrived, some with 

 the two hack molars entire. They confirm all the conclusions set forth in the 

 following pages, and especially the affinity of Plagiaulax and Microlestes. 



f The last back molar, whether of Microlestes or Plagiaulax, has two opposed 

 longitudinal marginal ridges, more or less lobed or crenated, and separated hy 

 a depressed disk. In the next or larger molar of Plagiaulax, the cusps are not 

 symmetrical on the two sides, there being two on the inner, and only one alter- 

 nating lobe on the outer ; and such seems to have been the case in the larger 

 imperfect tooth of Microlestes (c, fig. 3). 



